The incident occurred about 4:10 p.m. Sunday at Jesse Owens Community Regional Park in South Los Angeles, according to the Los Angeles Fire Department, which sent paramedics to help lifeguards administer aid and take the teenager to a hospital.

He was not breathing and had no pulse when pulled from the water.

The Fire Department provided few other details but family members spoke with KCAL9 about the incident.

Ceritha Daily said her brother, Anandre Thomas, had jumped into the pool and nobody noticed for about five minutes that he had failed to surface, despite there being four lifeguards on duty.

Daily said she saw Anandre jump, then turned to watch her other brother leap off a diving board.

It was several minutes before she noticed Anandre at the bottom of the pool, she said. She alerted lifeguards who pulled him out, began CPR and called for help.

Daily and Anandre's uncle, Tremon Thomas, said they believed he could have been saved if he had been noticed sooner. Now, they said, they have been told he is likely brain-dead.

The county Department of Parks and Recreation issued a statement that officials were "saddened to learn of the young man's condition, and our thoughts and prayers are with his family and friends at this difficult time."

Beyond saying the department "is fully committed to safety in our all our facilities and programs," parks officials said they could offer no further comment, citing an ongoing investigation by the county Sheriff's Department.

The investigation, parks officials said in the statement, "is moving forward with full respect for the privacy of the young man and his family and deference to the integrity of the investigative process."